text: The terminal oxide centers of polyoxometalate framework can in certain cases be replaced with other ligands, such as S, Br, and NR. Sulfur-substituted POMs are called polyoxothiometalates. Other ligands replacing the oxide ions have also been demonstrated, such as nitrosyl and alkoxy groups.
  Polyfluoroxometalate are yet another class of O-replaced oxometalates.